A capillary flow technique using capillary underfill (CUF) shown in FIG. 17 is a known example of a conventional flip-chip mounting method. This capillary flow technique begins with the application of flux (FIG. 17(a)). Next, a semiconductor chip such as an IC chip provided with a solder layer is placed on the flux (FIG. 17(b)). Subsequently, reflow soldering is carried out (FIG. 17(c)). Continuing, excess flux is cleaned off (FIG. 17(d)). Next, underfill is allowed to flow into the gap between the chip and substrate using capillary phenomenon (FIG. 17(e)). Finally, the underfill is thermoset by heat treatment (FIG. 17(f)).
However, in the case of this capillary flow technique, it is essential to use flux in addition to underfill. In addition, a flux application step (FIG. 17(a)) and flux cleaning step (FIG. 17(d)) are required. Consequently, in this capillary flow technique, it was not possible to efficiently mount a semiconductor chip. In the cleaning step (FIG. 17(d)) in particular, there were cases in which excess flux was unable to be completely washed off.
Thermal compression bonding (TCB), which uses a pre-applied underfill material (PAM) as shown in FIG. 18, is employed as a flip-chip mounting method that does not use flux application or flux cleaning steps. In this technique, a pre-applied type of underfill such as a non-conductive paste (NCP) is first applied to a substrate terminal (FIG. 18(a)). Next, a semiconductor chip provided with a solder ball is thermocompression bonded on the underfill (FIG. 18(b)). In addition to melting the solder ball of the semiconductor chip, this thermocompression bonding causes primary curing of the underfill. Subsequently, the underfill is subjected to secondary curing by undergoing heat treatment (FIG. 18(c)).
This thermal compression bonding technique requires only the three steps of applying the underfill, thermocompression bonding the semiconductor chip, and heat treatment, without using flux. Consequently, a semiconductor chip can be mounted efficiently.
In addition, Patent Document 2 describes a pre-applied semiconductor encapsulating film used in flip-chip mounting that comprises: (A) a liquid epoxy resin, (B) a thermoplastic resin, (C) a curing agent, (D) a latent curing accelerator subjected to heat treatment at 50° C. to 100° C., and (E) an inorganic filler.